Update nette/tester requirement from 2.5.5 to 2.5.6 (#182)

Updates the requirements on [nette/tester](https://github.com/nette/tester) to permit the latest version.
- [Release notes](https://github.com/nette/tester/releases)
- [Commits](nette/tester@v2.5.5...v2.5.6)

---
updated-dependencies:
- dependency-name: nette/tester
  dependency-version: 2.5.6
  dependency-type: direct:development
...

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Author: dependabot[bot]

composer.json

@@ -25,7 +25,7 @@
         "nette/utils": "^4.0.4@dev"
     },
     "require-dev": {
-        "nette/tester": "2.5.5",
+        "nette/tester": "2.5.6",
         "mockery/mockery": "1.6.12",
         "phpstan/phpstan": "2.1.28",
         "phpstan/phpstan-strict-rules": "2.0.6",